Polycarbonates have found many uses as a class of materials because they combine, in general, a high level of heat and impact resistance, good dimensional stability, and good insulating and non-corrosive properties. Halogenated polycarbonates and copolycarbonates are known especially for resistance to physical deformation at high temperature and resistance to flammability. Various examples of halogenated copolycarbonates are disclosed in the art, and I have found that these known compositions may be differentiated from the halogenated copolycarbonates of this invention in part by the character of the end groups possessed by the copolycarbonate molecules.
Representative examples of known halogenated copolycarbonates are found, upon analysis, to contain significant amounts of Phenolic End Groups, a Phenolic End Group being an -OH moiety at a copolycarbonate chain end, and/or Process Chemical End Groups, a Process Chemical End Group being the residue yielded at a copolycarbonate chain end by reaction with the copolycarbonate chain of a process chemical, such as a catalyst or other chemical which promotes, directs, regulates or otherwise influences the progress of the copolycarbonate forming reaction.
In addition to containing a significant amount of Phenolic and/or Process Chemical End Groups analysis also reveals that these representative halogenated copolycarbonates are characterized by a tendency toward thermal degradation, as evidenced by the formation of color bodies upon heating. Further, in the preparation of certain of these representative halogenated copolycarbonates, the reaction mixture is thoroughly emulsified by the time formation of the copolycarbonate product is complete, and several hours are required for the organic phase to separate from the emulsified mixture. It is difficult to readily wash an emulsified product-containing solution thoroughly enough to remove foreign material such as catalysts or inorganic salts, and the performance in a service environment of a product containing such foreign material is frequently impaired.
It would therefore be desirable to provide, and it is an object of this invention to provide, a halogenated copolycarbonate possessing an end group selectivity which has greatly reduced Phenolic and Process Chemical End Group content. It would also be desirable to provide a halogenated copolycarbonate which has improved resistance to degradation, such as can be caused by exposure to heating, and which possesses good washability.